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Polystyrene caps
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IvoS:
I have a low THD 10kHz oscillator PCB board that has populated polystyrene capacitors. It needs to be cleaned very well from flux residue because it is using current feedback OPamps. Any PCB leakage and flux residues usually causing high frequency oscillation. I use medical grade 91% isopropyl alcohol (got it from walgreens). The question is, can submerge the whole board with those polystyrene caps as well? The other parts on the board should be no problem.
Thanks.
Ian.M:
http://kmac-plastics.net/data/chemical/polystryrene-chemical-resistance.htm

It looks like it should be OK.  Don't leave it immersed overnight!  Caution: the markings may come off.
bd139:
Check the trimpot data sheets as well.
exe:
Is this really needed? How big is feedback current?

I don't encourage people leave flux on the pcb, but I  prefer using "no clean" fluxes that are non-conductive and non-corrosive (but don't trust package labels, not all no-clean fluxes are really no-clean). That's because cleaning flux from underside of ICs can be a challenge.

(of course, for low-leakage applications leaving flux is not an option).
Ian.M:

--- Quote from: bd139 on June 17, 2018, 02:46:00 pm ---Check the trimpot data sheets as well.

--- End quote ---
Yes.  If the pots aren't fully sealed and resistant to IPA you are in for a whole world of grief (or even if you put a hot board into cold IPA so the internal air pressure change overwhelms their seals).   If necessary, de-solder them, clean the rest of the board then re-solder them with minimal flux, and spot-clean round them with IPA, brushes and Q-tips.
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